"Historic?" The owner of this Houston Street gas station needed Landmarks approval to replace it with a tiny new building.Steve Cuozzo

The war raging over whether to landmark a few dozen buildings in East Midtown obscures a more critical preservation issue for the next mayor: the mushrooming of whole districts where landmarking rules make redevelopment difficult to impossible.

An astounding 27.7 percent of all Manhattan buildings fall under Landmarks Preservation Commission rules when so-called “historic districts” are included, according to the Real Estate Board of New York, an industry lobbying and advocacy group. That’s more than twice the oft-cited figure for individual landmarks of 12 percent.

Moreover, says REBNY President Steven Spinola, the number of affected buildings below 110th Street is a much higher 36 percent.

Thus, in those parts of Manhattan where new development would most likely occur, nearly four properties in 10 either can’t be torn down (if they’re individual landmarks) or can be replaced only with extreme difficulty and in conformity with the LPC’s whim (if they’re in historic districts).

Even those sobering numbers likely understate the true picture. REBNY counted not actual buildings but tax lots which are either in a historic district or have an individual landmark — yet several buildings can occupy one tax lot.

Under Mayor Bloomberg, the number of historic districts has grown 32 percent citywide and 26 percent in Manhattan. Spinola might exaggerate in saying, “The city is landmarking away its economic future.” But consider: Manhattan historic districts even include no fewer than 48 vacant lots and 50 parking lots, where existing zoning would allow about 2.6 million square feet of new construction.

Among them: a gas station at Lafayette and West Houston streets, which just falls within the confines of the SoHo-Cast Iron Historic District Extension established in 2010. It’s finally going to be demolished, but its owner had to go through hoops to win the LPC’s blessing to replace it with a tiny, 7-story office building.

The panel has often prevented new buildings from rising to their legally permissible sizes and heights by rejecting proposals that it deemed not “appropriate.”

In the West Village and on the Upper West Side, an astounding 70 percent of properties are either landmarks or part of historic districts, REBNY found. Both are among the world’s most desirable neighborhoods, but if it’s near-impossible to put up normal-size new apartment buildings there, it’s hard to blame developers from chasing the high-end market with 80-story towers at sites outside LPC’s purview.

The City Planning Commission at long last is trying to up-zone the Grand Central area. But the LPC has effectively usurped the planners’ authority, claiming it isn’t allowed to weigh economic impact in deciding which blocks to declare “historic.”

And while the Planning Commission theoretically has a say when a proposal to create or expand a historic district reaches the City Council, it’s loath to contradict the landmarks panel publicly.

Nobody wants to level truly distinguished blockfronts. But new development typically creates jobs and generates precious tax revenue. To help the city more rationally reconcile the imperatives of preservation and growth, the Planning Commission should be involved much earlier in the landmarking process.

Otherwise, the destiny of vast parcels will be entirely up to preservationist sages who can’t often agree on the qualities of even a single building.

Yes, developers would build skyscrapers in Central Park if they could. They’d have us believe new construction is being thwarted everywhere despite the sight of cranes at scores of locations.

But when development is needed both to alleviate the housing shortage and to create new homes for major companies, the REBNY data are a strong indictment of the preservationist agenda swallowed by many elected officials.

Bloomberg deserves great credit for opening up many parts of town for new construction — at Hudson Yards, and in former “manufacturing” areas in the outer boroughs.

But those breakthroughs blind many to the LPC’s ever-tightening straitjacket on central Manhattan. The city’s and the nation’s economic and cultural heart needs more freedom to change and grow.